Do not use build_data if not needed

Author: Olli-Pekka Puolitaival

mbed/mbed.py

@@ -2680,7 +2680,8 @@ def test_(toolchain=None, target=None, compile_list=False, run_list=False, compi
         if build_data:
             # Preserve path to given build data
             build_data = os.path.relpath(os.path.join(orig_path, build_data), program.path)
-        else:
+        elif icetea_supported:
+            # Build data needed only if icetea is supported
             # Create the path to the test build data file
             build_data = os.path.join(build_path, 'build_data.json')